As is well known in this technology, the design of radial-inflow turbines relies primarily upon general empirical guidelines developed from previous successful designs and experience gained in the field. These guidelines dictate the sizing of the flowpath, blade tip diameter, rotor axial length, blade number and blade shape. The disadvantage of this approach is that resulting designs generally feature relatively low aerodynamic loadings, are heavy and have high rotational inertia. The relative mass of the turbine generally leads to increased disk bore stresses which limit the turbine's life, and restrict the turbine from operating at high tip speeds that would ordinarily be required for advanced applications.
Traditional radial-inflow turbine blades are developed by axially stacking a number of two dimensional cross-sections which satisfy thickness requirements and are set at various wrap angles. The disadvantage of this blade generation method is that the airfoil's surface is not developed in the streamwise direction. As a result, surface contours and curvatures may not be smooth and continuous.
AIAA Publication AIAA-91-2127 entitled "DESIGN AND EXPERIMENTAL EVALUATION OF COMPACT RADIAL-INFLOW TURBINES, by A. J. Fredmonski, F. W. Huber (co-inventors of this patent application), R. J. Roelke and S. Simonyi presented at the joint AIAA/SAE/ASME/ASMEE 26TH Joint Propulsion Conference discloses a radial-inflow turbine that has been designed using a multi-stage three-dimensional (3-D) Euler solver. The Euler solver allows the aerodynamic design of the airfoil of the turbine and according to this paper the design had a 40% less rotor length than current traditionally-sized radial turbines. To achieve this size reduction a unique calibrated 3-D multi-stage Euler code (not discloses in this paper) was devised and applied to accurately predict and control the high rotor flow passage velocities and high aerodynamic loadings resulting from the reduction in rotor length. The objective of the paper was to compare the advanced design to current state-of-the-art configurations.
Absent from this paper are the parameters, dimensions and the methodology that are necessary to arrive at a design of the radial-inflow turbine. The codes are a result of fully three-dimensional computational fluid flow dynamics and techniques and are necessary to arrive at a significant size reduction and maintain high performance. In order to arrive at the codes, a compilation of airfoils are computed and analyzed aerodynamically in order to generate curves in non-dimensional values that exhibit the necessary wrap distribution. This invention teaches the method of designing the rotor's wetted surface of a radial-inflow turbine by utilizing a predetermined wrap distribution and relating it to the aerodynamic flowfield, such that the rotor maintains high aerodynamic performance. The reduction in size, the reduction in inertia and the high aerodynamic performance are attributed to the rotor's predetermined wrap distribution and leading edge shape obtained from prescribed, normalized relations.